This invention relates generally to homopolar electrical machines utilizing liquid metal current collectors, and more particularly to a porous, compliant structure interposed between rotor and stator collector rings to maintain electrical contact therebetween and permit such machines to operate with a liquid metal contact under a broad range of operating conditions.
Homopolar machines, which are used both as generators and motors, commonly include a rotationally supported rotor collector assembly concentrically enclosed by a stationary stator collector assembly. The rotor structure normally includes a plurality of radially extending circumferential tips or flanges, wherein each flange is designed to project into a conforming channel formed in the interior surface of the stator such that a radial gap is defined therebetween. Liquid metal is placed in the channels of the stator to span the radial gap and form an electrical contact. Accordingly, as the rotor rotates relative to the stationary stator element, electrical currents are able to pass through the liquid metal contact, between the circumferential flanges of the rotor and the surfaces of the stator channels. Although such arrangement generally allows the use of larger current densities and higher rotational speeds than electrical machines employing common electrical brushes, one problem associated with homopolar machines employing liquid metal contacts involves Lorentz forces produced by electrical currents passing through the liquid metal in the presence of magnetic fields. One effect of such forces is the tendency of the liquid metal to be pushed or expelled from the stator channel such that the contact area between the rotor and stator is reduced. Prior art, as illustrated by U.S. Pat. Nos. 3,984,715; 3,989,968; 4,027,184; and 4,146,807 rely upon means for maintaining or recirculating the liquid metal between the rotor flange and the stator channel. Further, U.S. Pat. Nos. 3,681,633 and 3,796,900 use pressure and centrifugal force to expel liquid metal from hollow rotor passages into collecting means in the stator or stationary member such that electrical contact is maintained therebetween.
Another problem encountered with homopolar machines is the viscous drag effects which occur in the liquid metal as the rotor flanges move through the respective stator channels and tend to reduce the operational speeds of the machines. One proposal for overcoming the drag effects is set forth in U.S. Pat. No. 3,604,967 which discloses a floating ring means immersed in a liquid metal to increase the rotor speeds by reducing the relative velocities between the liquid metal and the adjacent surfaces of the rotor and stationary members.